1. Field of the Invention
The present invention relates to a pivotally movable guide for use in a power transmission device including an endless chain trained around a driving sprocket and a driven sprocket, or a similar power transmission device including an endless belt trained around a driving pulley and a driven pulley. More particularly, it relates to a pivotally movable plastic guide used as a tensioner lever or a guide lever pivotally mounted on a single shaft in the power transmission device.
2. Description of the Related Art
In general, an engine or a driving unit includes a power transmission device for transmitting power by means of a chain or a belt. In the chain or belt power transmission device, a pivotally movable guide having slip function is used. The movable guide is mounted to a body of the engine or driving unit by means of a mounting bolt or a pin.
In use, the movable guide is held in slide contact with an endless chain or belt while running so as to apply an appropriate tension to the chain, or to prevent whipping and lateral oscillation of the chain or belt during travel.
FIGS. 16 to 18 show a conventional movable plastic guide 100 used in a chain drive system, the guide taking the form of a tensioner lever. The guide 100 has a one-piece structure molded of a single synthetic resin material and includes a curved shoe 101 for slide contact with a chain C, a thin plate-like guide body 102 disposed on the back side of the shoe 101 along the length thereof and extending perpendicularly to a front surface (shoe surface) of the shoe 101, a side flange 103 disposed on and along a side edge of the guide body 101 opposite to the shoe 101, and a boss 105 formed at one end of the guide body 102 and having a mount hole 104 for attachment of the guide 100 to the body of an engine or a driving unit. Reference numeral 102xe2x80x2 denotes reinforcement ribs formed on front and rear surfaces of the thin plate-like guide body 102.
Due to the one-piece structure molded of a single synthetic resin material, the conventional movable plastic guide 100 is unable to maintain its slip properties, wear resistance, strength properties at high levels in a compatible manner. For instance, when a synthetic resin material with excellent slip properties and wear resistance is used, the resulting movable guide has an insufficient mechanical strength. Alternatively, enlarging the cross section to recover the insufficient mechanical strength results in a guide with undue thickness, which requires a large space for installation of the guide to the body of the engine or driving unit.
To deal with this problem, several improvements have been proposed. According to one improvement disclosed in Japanese Patent No. 2,818,795, a plastic guide is formed by a support member of fiber reinforced plastic and a lining member of high wear-resistant plastic, wherein the support member and the lining member are produced in a progressive molding cycle and are interconnected via one or several dovetailed connections. According to another improvement disclosed in Japanese Patent Laid-open Publication No. 8-254253, a plastic guide is formed by insert molding, wherein an extruded steel core or insert is molded with synthetic resin. Both the progressive molding process and the insert molding process require a complicated molding die assembly, which increases manufacturing cost of the plastic guides. Additionally, due to the difference in thermal expansion coefficient between two different plastic materials or between the plastic material and the steel core, the guide is likely to deform or sometimes break.
Still another prior improvement is shown here in FIGS. 19 to 21, wherein a movable plastic guide 110 is formed by a curved plastic shoe 111, a plastic guide body 111 integrally molded with the shoe 111 and a reinforcement plate 118 of steel or iron fitted in a groove 117 formed in a front surface of the molded shoe 111. The guide body 112 has reinforcement ribs 112xe2x80x2 and a side flange 113. The reinforcement plate 118 is arranged in parallel with a curved shoe surface of the molded guide body 111, so that the modulus of section of the movable guide 110 is relatively small and this deteriorates the rigidity and strength of the movable guide 110. Especially, since a mount hole 114 extending through a boss of the molded guide body 111 is distant from, and hence is not reinforced by, the reinforcement plate 118, as shown in FIGS. 19 and 20, the strength of a molded guide body portion extending around the boss is very low. Additionally, the curved reinforcement plate 118 made of metal requires a punching process followed by a bending process, which increases the manufacturing cost of the movable guide 110.
According to another prior improvement, a movable guide is formed by a guide body made of metal or fiber reinforced plastic and a plastic shoe that are formed separately and are interconnected via a mechanical connection such as hooks formed on the shoe (see Japanese Utility Model Publication No. 7-36201, Japanese Utility Model Registration No. 2,519,476 and Japanese Patent Laid-open Publication No. 9-324839). The two-piece guide is complicated in construction, is not readily adapted to an automated assembling process, requires relatively high manufacturing cost, and may cause accidental separation of the guide body and the shoe due to a damage at the mechanical connection.
According to still another prior improvement, a guide has a plastic guide body sandwiched between metal plates (see Japanese Patent Laid-open Publications Nos. 11-2012249, 11-22790 and 2000-220706). The guide of the laminated structure is costly to manufacture due to parts variety and increased assembling man-hours.
It is, accordingly, an object of the present invention to provide a pivotally movable plastic guide for a power transmission device, which includes a plastic guide body of a simple configuration and a reinforcement plate of a simple configuration arranged to enlarge the modulus of section of the guide to thereby increase the flexural rigidity and strength of the guide without increasing the cross-sectional dimensions and overall weight and size of the guide, which occupies a relatively small space for installation with respect to a fixed support member such as an engine body, and which is free from break or rupture caused due to the difference in thermal expansion coefficient between the guide body and the reinforcement plate.
To achieve the foregoing object, according to the present invention, there is provided a guide for a power transmission device including an endless chain or belt, the lever comprising: an elongated one-piece guide body molded of synthetic resin, the guide body having a shoe at one longitudinal edge thereof and a plate-like carrier integral with the shoe. The shoe has a shoe surface for slide contact with the chain or belt, and the carrier extends from the shoe in a direction perpendicularly away from the shoe surface and has a longitudinal groove extending along the length thereof and opening to a longitudinal edge of the carrier facing away from the shoe surface. The carrier further has a mount hole formed at one end thereof for attachment of the guide to a stationary mount base. The guide further comprises a reinforcement plate fitted in the longitudinal groove of the carrier and having a through-hole at one end thereof, the through-hole being aligned the mount hole of the carrier.
The guide body including a shoe and a carrier integrally molded from synthetic resin into a one-piece structure has slip function. The carrier has a longitudinal groove extending along the length thereof and opening to a longitudinal edge thereof facing away from the shoe surface. With the reinforcement plate fitted in the longitudinal groove of the carrier, the guide has high flexural rigidity and strength. The reinforcement plate can readily be assembled with the guide body merely by being inserted into the longitudinal groove in the carrier. Such simple assembling process lowers the manufacturing cost of the guide and is particularly suitable for automated assembly of the guide.
The guide body and the reinforcement plate are connected together at one end when the guide is mounted to a stationary mount base by means of a shouldered bolt or a pin extending through the mount hole in the carrier and the through-hole in the reinforcement plate. With this arrangement, the opposite end of the reinforcement plate is kept free in the longitudinal direction thereof within the longitudinal groove of the carrier. Accordingly, even when the reinforcement plate undergoes thermal elongation relative to the guide body, such thermal elongation does not cause breaking or rupturing of the guide body.
In one preferred form of the present invention, the longitudinal groove is closed at one end so as to form a pocket in the guide body, and the reinforcement plate having an end portion received in the pocket with a gap formed between the end portion of the reinforcement plate and a corresponding end portion of the guide body. The end portion of the reinforcement plate is located remotely from the through-hole.
The guide body and the reinforcement plate may be interconnected by a snap-fit connection. The carrier may have a locking nose projecting into the longitudinal groove at a position adjacent to the longitudinal edge of the carrier, and the reinforcement plate has a rear edge interlocked with the locking nose. As an alternative, the carrier may have a locking projection projecting into the longitudinal groove, and the reinforcement plate has a recessed portion complementary in contour to the shape of the locking projection and interlocked with the locking projection.
The reinforcement plate may have a plurality of openings formed therein, or a plurality of parallel spaced hollow spaces extending transversely across the width of the reinforcement plate, so as to reduce the overall weight of the guide.
The reinforcement plate may be folded on itself and have a substantially U-shaped cross section having two, parallel spaced wing-like body portions, and the guide body has two laterally spaced longitudinal groove extending along the length of the carrier and opening to a longitudinal edge of the carrier facing away from the shoe surface, the body portions body portions of the folded reinforcement plate being fitted in the longitudinal grooves, respectively. As an alternative, the reinforcement plate may be comprised of two reinforcement plates members of identical configuration, the reinforcement plates members being fitted in the longitudinal groove of the guide body in a superposed condition or in two lateral spaced longitudinal grooves formed in the guide body.